We treated young and aged C57BL/6 mice with 1mg/mL of NAC delivered via drinking water in 7 cohorts that included 3 young mice and 1 old mouse per group. 7 age-matched control cohorts were also included in the experiment. After exposure to the antioxidant for one month, the treated and untreated young and old age-matched mice were sacrificed. Bone marrow analysis was performed after the administration of this antioxidant for a four week period. Two independent competitive transplant experiments were performed. 200 donor HSCs from young NAC treated, young control, old NAC treated, or old control mice were transplanted against 4x105 congenic (CD45.1) whole bone marrow cells into lethally irradiated recipient mice. FLARE comet assays, that measure oxidative damage, are being performed on HSCs purified from treated and untreated mice. We have continue to maintain calorie restricted (CR) C57BL/6 mice from the NIA aged rodent colony and ad-lib fed age-matched mice to 24 months of age. Analysis of the bone marrow of these aged CR, aged ad-lib fed, and young mice was performed and HSCs were purified to examine damage accumulation.